Hello,
Alright I'm having a heck of a time with my old 94. About 2 years ago the front tank just stoped working. I assume it was the pump. I started running it off the rear tank and never had a problem till about three weeks ago it wouldnt start. So I asked around and was told replace the pump and I did. Still wouldn't start. I ended up having to replace the fuel selector switch and after that it started right up. I went to drive to my parents put 6 gallons in and after 10 miles it started sputtering and acted like it was running out. I've now found that the gas is going from the rear to the front tank. I never had this problem before I changed the rear pump. I guess my question is does anyone know why its doing it and how to fix it. Could it be a valve? If so where is it ? Could the new pump be bad? Any help or ideas would be great.
Thank you in advance
Bo

 

Hey Bo. I have had two new pumps go out in my bronco, one after just a few hours and one after two days. That was my first car and you wouldn't believe the words that came out of my dad's mouth . "Chinese !@#$% so and so !@#$% parts" I remember was one of his favorite sentences. So yeah, it wouldn't surprise me if a new pump went bad, it happens. Other than that I would just double check that you have the return lines connected right being you replaced the tank switch. I've done it.......

 

Very common problem on these trucks, it's referred to as fuel transfer or crossflow. There is a small valve in each fuel delivery module in each tank. The front tank FDM has a bad shuttle valve in it which allows the rear pump (FDM) to fill up the front tank. There was a recall for it at one time.

Excessive fuel pressure can also cause the problem too. There was also a recall to replace the Fuel Pressure Regulator on some vintage trucks back in the day.

Looks like it may be time to replace the front fuel pump assembly.

 

Hey ford community, I have a 1994 ford f150 XLT 5.0 with 112,000 on the dash. I'm wondering if anyone knows what the deal with the tanks are. It seems that if I fill the back tank it fills the front tank. The problem here is that something is wrong with my main tank other then filling up from the rear then overflowing. I usually have a tough time accelerating (seems kinda sluggish). My rear tank on the other hand runs fine accelerates no problem. Does this sound like a fuel pump issue on my main tank or selector valve. Any help is appreciated.

 

Welcome to FTE!

You should have opened your own thread for this VERY common issue.

First off there is no selector valve on your truck. The tank getting filled (front in your case) has a bad valve in it which allows the fuel from the rear tank to fill the front. It's commonly called cross-flow and happens quite often. Almost everyday someone posts with the same symptoms.

The fix is to replace the front Fuel Delivery Module (FDM).

The part that is causing the issue is the high pressure check valve in the FDM:


You can't get just that piece to the best of my knowledge.

A good photo of it from Subford:

 

I’m having the same exact problem with my 94 f150 , I put gas in my back tank (my back tank works flawlessly ) and then I notice it does last at all and my front tank is full ... what’d you end up doing to fix it?? Anyone fixed this?

 

post #3, #5 by rla2005, is your answer/fix

 

My dad's 94 has this issue, but he said that the fuel is going to the rear tank instead of the front tank. Is that a bad fuel pump/sender assembly? And if so, which one is bad in this case?

Also, did I read that right - no selector valve on a 94 f150? How does the switch select between tanks if there's no selector valve?

 

Yes and Its always the FDM in the tank recieving fuel.

'89 was last year for the selector valve on gasoline trucks. The switch simply powers up the pump in one tank or the other, the check valve and shuttle valve inside the FDM(see diagram above) in each tank prevent crossflow.. when working correctly.